The present invention relates generally to digital imaging systems and, more particularly, to a calibration and setup procedure for determining a separation distance between a radiation source and a digital detector in a digital imaging system.
The installation and setup procedures for digital imaging systems, such as radiographic diagnostic imaging systems, can be complex and time-consuming. For example, to comply with customer image quality and consistency requirements and various regulatory and safety standards for diagnostic imaging systems, such procedures generally require the determination of a variety of factors, including the accurate positioning of the x-ray source with respect to the x-ray detector. For instance, the determination and establishment of fixed setpoints (or detent positions) for setting the separation distance between the x-ray source and x-ray detector and calibrating the system such that an accurate readout of the separation distance can be obtained often are required procedures. The determination and establishment of this separation distance, referred to as the source-to-image distance (SID), assists in appropriately controlling the size of the x-ray field during diagnostic use of the imaging system. Further, many regulatory requirements specify that the SID must be clearly displayed to the operator or user of the system with a certain level of accuracy.
Generally, known installation and calibration procedures for establishing fixed SID setpoints and corresponding SID readouts, require the presence of a field engineer who, through a trial and error process, calibrates the radiographic imaging system and installs fixed, preset detent positions that lock the x-ray source into various repeatable separation distances from the detector. For example, the field engineer may install an electromechanical switch, or other device, in the ceiling or the superstructure of the x-ray source that indicates to the user in a tactile or otherwise perceptible manner that the x-ray source is at one of the preset SID positions. Many radiographic imaging systems include industry-standard SID setpoints at separation distances of, for example, 40 inches, 60 inches, and 72 inches.
The installation and calibration procedure, however, becomes even more complex if the detector also is non-stationary. In such event, the field engineer must repeat the setup and calibration procedure at multiple detector positions and install several setpoint or detent devices at the corresponding multiple determined SID positions.
Once the preset SID positions are determined and marked with a detent device, the SID positions are fixed. Thus, a user of the imaging system is not afforded flexibility in the event that the user may desire an SID position that is non-standard. Accordingly, even though either the x-ray source or the x-ray detector could be moved to a variety of different positions such that patients of various sizes could be accommodated or various anatomical parts could be more easily imaged, the actual positions in which the x-ray source could be located with respect to the x-ray detector are restricted to only those few positions which have corresponding fixed detent setpoints.
Preset fixed setpoints can also result in decreased system reliability because the physical switches or detent devices increase the number of components which can potentially fail during system usage.
Thus, it would be desirable to provide a system and method for installing and calibrating a digital radiographic imaging system that would avoid time-consuming iterative procedures for determining fixed SID positions and for providing a calibrated readout and display of the actual SID. It would be further desirable if such a system and method would result in the elimination of, or reduced reliance on, fixed setpoints and physical fixed setpoint devices, thus affording greater flexibility and increasing the reliability of the system.
The present invention addresses one or more of the shortcomings noted above.
For example, a method for determining a setpoint for setting the separation distance between a radiation source and a digital detector in a digital imaging system includes positioning the radiation source with respect to the detector at a first source position, sensing the first source position and providing a first feedback signal representative thereof, and generating a first radiation beam having a beam angle. The first beam is detected on the detector and the size of the impact area of the first beam is determined. The source is then displaced to a second source position and a feedback signal representative of the position is generated. A second radiation beam having substantially the same beam angle as the first beam is generated while the source is at the second position. The second beam is detected on the detector and a size of the impact area of the second beam is determined. A separation gain constant is then determined based on the displacement of the source and the first and second feedback signals representative of the source positions. A separation distance between the source and the digital detector based on the sizes of the impact areas and the source displacement also is calculated. The separation gain constant and the calculated separation distance can then be utilized to position the radiation source at a selected source-to-image distance (SID).
In another aspect of the present technique, a method for determining a separation distance between a radiation source and a digital detector positioned to detect a radiation beam generated by the source is provided. A first beam is generated with the source positioned at a first source position and a size of a first impact area of the first beam detected on the detector is determined. A system parameter is then varied such that a second radiation beam generated by the source has a second impact area on the detector, the second impact area having a second size that is different from the first size of the first impact area. The second beam is then generated and the second size of the second impact area of the second beam is determined. A first separation distance of the radiation source with respect to the detector is computed based on the determined first and second sizes of the first and second impact areas and the value of the varied system parameter.